In brief–Research news and discovery

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THE collision of entire clusters of galaxies has helped set the firmest limit yet on the amount of antimatter in the universe.

In the early universe, the theory goes, matter and antimatter should have been created in equal amounts. However, our universe appears to be made of matter – though astronomers have never been able to rule out the possibility that there are

antimatter galaxies out there.In 2006, astronomers

discovered the Bullet cluster – two clusters of galaxies that had collided, leaving a giant cloud of hot gas. If any fraction of this gas is a mixture of matter and antimatter, then collisions between these particles should result in mutual annihilation, producing gamma rays instead of the X-rays expected from collisions

between matter particles.Gary Steigman of Ohio State

University in Columbus now says that the amounts of X-rays and gamma rays emitted from the Bullet cluster prove that the fraction of “mixed matter” is less than a few parts per million (www.arxiv.org/abs/0808.1122v1).

Steigman reckons this excludes the possibility that a significant amount of antimatter exists on scales up to about 65 million light years, but cannot rule out finding it at larger scales.

What’s the matter in galactic clusters?

MALARIA’s ability to infect species as diverse as humans, birds and mice led us to assume that species-specific parasite strains had slowly evolved along with their hosts. Now it seems that the explosion in vertebrate diversity happened well before the parasite was able to infect them, ruling out the co-evolution theory.

Vertebrates began to split from each other about 310 million years ago. But Toshiyuki Hayakawa at Osaka University in Japan and colleagues analysed the parasite’s mitochondrial genes and found that modern strains suddenly diverged from a common ancestor only 38 million years ago. In an upcoming paper in Molecular Biology and Evolution, the team say the spurt occurred when the parasite learned to switch hosts.

Malaria’s big bang pinpointed

A GIANT ring of debris around a nearby star appears to be a much bigger version of our solar system’s Kuiper belt, the region of ice-rich objects beyond Neptune that is thought to be a source of comets.

A team led by Christine Chen of the Space Telescope Science Institute in Baltimore, Maryland, used the orbiting Spitzer Space Telescope and the Gemini South telescope in Chile to study infrared light from the disc around HD 181327, which lies about 150 light years from Earth. They saw a peak in brightness at a wavelength of around 63 micrometres, which is characteristic of water ice. “We now have evidence that the composition is similar to our Kuiper belt,” says Chen.

The disc has a radius of about 12 billion kilometres, roughly twice the size of the Kuiper belt. It is also exceptionally bright, suggesting that it holds a lot of material – so the system may be swarming with comets.

Kuiper belt twin

THEY may not look much like ballerinas, but elephants are more nimble-footed than their cumbersome frames suggest.

Previous studies had assumed that elephants walk with relatively straight legs, stiff ankles and flat feet. To investigate whether this is true, John Hutchinson from the Royal Veterinary College in London filmed 15 African and Asian elephants with reflective tape stuck to 10 key joints on their bodies.

Software then tracked the motion of the reflective markers to build 3D models of how the animals’ skeletons

move underneath their thick skin.The models revealed that although elephants do tend

to walk on the flats of their feet, they also roll from their heels to their toes while running, just as humans do (The Journal of Experimental Biology, vol 211, p 2735). The ankles act like a spring, propelling them forward.

“When they walk slowly the legs are fairly straight, but as they get faster, the joints are more bent, so their posture is more crouched,” says Hutchinson.

He hopes that vets could use a similar method to detect whether an elephant is walking with an abnormal gait. Simulations of dinosaur locomotion are often based on the way elephants move, so Hutchinson’s work may improve their accuracy.

The need for speed keeps elephants on their toes

14 | NewScientist | 30 August 2008 www.newscientist.com